Zinc plating baths

ABSTRACT

A brightening composition for the lustrous deposit of zinc from alkaline cyanide solutions contains the condensation products formed by reaction of dialdehydes with polyamine salts. The polyamines of the polyamine salts have at least two terminal amine groups on an aliphatic chain. The salt is formed by neutralizing a water soluble acid with the water soluble polyamine. Reaction of the polyamine salt with the dialdehyde produces the novel condensation products.

United States Patent 1 Grossblatt 51 May 13, 1975 ZINC PLATING BATHS [76] Inventor: Gerald H. Grossblatt, 3041 Hudson Ct., Chamblee, Ga. 30033 [22] Filed: July 10, 1972 [21] Appl. No.: 270,185

[56] References Cited UNITED STATES PATENTS 1/1950 Chester et a1 204/55 Y 6/1954 Diggin et a1. 204/55 Y 3,472,743 10/1969 Rushmere ..204/55Y Primary Examiner-G. L. Kaplan [57] ABSTRACT A brightening composition for the lustrous deposit of zinc from alkaline cyanide solutions contains the condensation products formed by reaction of dialdehydes with polyamine salts. The polyamines of the polyamine salts have at least two terminal amine groups on an aliphatic chain. The salt is formed by neutralizing a water soluble acid with the water soluble polyamine. Reaction of the polyamine salt with the dialdehyde produces the novel condensation products.

12 Claims, N0 Drawings ZINC PLATING BATHS FIELD OF THE INVENTION The present invention relates to condensation products. for addition to alkaline cyanide zinc plating baths in order to produce lustrous bright deposits over wide current density ranges, and to methods for the preparation of such condensation products.

BACKGROUND OF THE INVENTION In electroplating, a cell is charged with an electrolyte having the particular metal to be plated dissolved therein. The cell is equipped with anodes, usually at each end thereof, with the material to be plated serving as the cathode. Current flow between the anode and cathode deposits the metal to be plated on the cathode. Conventional solutions for the electrodeposition of zinc can be classified into two categories: the acid zinc baths, such as those containing zinc sulfate, zinc chloride, zinc fluoborate and the like; and the alkaline zinc baths containing zinc oxide, with and without sodium cyanide, and sodium hydroxide. The electrodeposit of zinc is generally dull. Brightening agents are necessary for a lustrous appearance. Brightening agents are seldom suitable for baths of both acid and alkaline baths.

A wide variety of brightening agents have been successfully used; however, most have not been completely satisfactory. Some brightener compositions are not stable in the plating bath. Some brightening agents formed of condensation products have had drawbacks as to solubility, incomplete activity, thermal breakdown, and limited to use either in alkaline high cyanide zinc plating baths or alkaline low cyanide zinc plating baths. Moreover, some brightening agents perform satisfactorily only over a narrow current density range.

Other agents exhibit poor stability in the plating bath.

SUMMARY OF THE INVENTION A principal object of the present invention is the preparation of polyamine-aldehyde condensation products of high activity as brightening agents and which possess thermal stability.

Another principal object of the present invention is the formation of condensation products that can be added to high, medium, or low cyanide zinc plating baths for producing lustrous bright deposits over wide current density ranges.

A further object of the present invention is to prepare water soluble condensation products that are highly stable in the alkaline cyanide zinc plating baths.

Other objectives and advantages of this invention will be apparent from the following description and appended claims.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION The present invention is directed to obtaining a bright zinc coating by electrodeposition in an aqueous,

tion products in alkaline cyanide zinc baths produce lustrous bright deposits over wide current density ranges.

The polyamine salt is prepared by neutralizing a water soluble acid with a water soluble aliphatic polyamine having two terminal amine functional groups. Typical polyamines for preparing the salt may be represented by the formula:

in which R is an aliphatic chain containing from 2 to 5 carbon atoms between the terminal amine groups, and R and R" are hydrogen or aliphatic substituent groups which do not adversely affect the water solubility of the amine salt. R and R" for example may be alkyl or alkene substituents having 2 to 5 carbon atoms, diaminoalkyl, or diamino-alkene groups.

Typical examples of suitable polyamines include alkylenepolyamines, aliphatic diamines, and derived aliphatic diamines, but are not limited thereto, and are represented by the following:

1,2 Diamino ethane 1,3 Diamino propane 1,4 Diamino butane 1,5 Diamino pentane 1,2 Diamino propane Bis (3-aminopropyl) methylamine 3,3 Diamino-dipropylamine Diethylenetriamine Triethylenetetramine Tripropylenetetramine Dipentylenetriamine Dibutylenetriamine Pentaethylenetetramine The acids used in the practice of the present invention to form the neutralized polyamine salts are water soluble, and can be either organic or inorganic. The main requirement is that the acid form stable electrovalent bonds with the polyamine without decomposition for enabling a controlled formation of highly active condensation products when heated with dialdehydes. Typical examples of suitable acids are the following:

Citric acid Hydroxyacetic acid Acetic acid Monosodium phosphate Sodium Acid sulfate Monochloroacetic acid Proprionic acid.

The salts are formed conveniently by adding the polyamine to a water solution of the acid in sufficient amounts to neutralize the acid. After preparation of the polyamine salt, the condensation products are formed by reacting the polyamine salt with a dialdehyde. This may be performed by adding the dialdehyde to a water solution of the polyamine salt and heating to temperatures and for a time for the condensation to occur.

The dialdehyde is a water soluble for reaction with the polyamine salt. Suitable dialdehydes have terminal aldehyde groups as represented by the following formula:

Ol-lCRCHO in which R is an aliphatic group containing from to 3 carbon atoms in the chain linking the aldehyde groups.

Suitable dialdehydes within the above formula for reaction with the polyamine salt are the following:

Ethanedial Pentanedial 2,4 Dimethyl pentanedial Butanedial 2 Methyl pentanedial 2,5 Diethyl pentanedial 2,3 Dimethyl butanedial The condensation reaction between the dialdehyde and the polyamine salt is conveniently conducted by introducing the dialdehyde into a water solution of the polyamine salt, and then heating at temperatures and for a time sufficient for the production of condensation products.

The reaction proceeds more rapidly at elevated temperatures, for example in the range from about 150 to 200F., although temperatures in the broad range from ambient to the boiling point may be used. The reaction ordinarily is completed within 15 minutes at temperatures in the range from 170175F., although it will be realized that longer reaction times will be needed at lower temperatures.

Examples of methods for making the water soluble condensation products employed in the invention are as follows:

EXAMPLE NO. 1

2.6M of sodium acid sulfate were dissolved in 0.45 liter of water. 1.3M of 1,4 diamine butane were added slowly while mixing. After the neutralization was complete, the mixture was heated to 150F. and 1.3M of ethanedial were added. The mixture was then heated to 170-l75F. and allowed to react for minutes and then cooled to room temperature. The result was a water soluble condensation product.

EXAMPLE NO. 2

2.8M of acetic acid were dissolved in 0.44 liter of water. 1.4M of diethylenetriamine were added slowly while mixing. After the neutralization was complete, the mixture was heated to 150F. and 1,4 butanedial were added. The mixture was then heated to 170175F. and allowed to react for 10 minutes and then cooled to room temperature. The result was a water soluble polymer condensation product.

EXAMPLE NO. 3

3.0M of citric acid were dissolved in 0.44 liter of water, 1.5M of 1,2 diamino propane were added slowly while mixing. After the neutralization was complete the mixture was heated to 150F. and 1,5M of pentanedial was added. The mixture was then heated to l-175F. and allowed to react for 10 minutes and then cooled to room temperature. The result was a water soluble condensation product.

EXAM PLE NO. 4

2.4M of proprionic acid were dissolved in 0.45 liter of water. 1.2M of 1,3 diamine propane were added slowly while mixing. After the neutralization was complete the mixture was heated to F. and 1.2M of 2,4 dimethyl pentedial were added. The mixture was heated to 175F. and allowed to react 10 minutes and then cooled to room temperature. The result was a water soluble polymer condensation product.

EXAMPLE NO. 5

3.2M of monosodium phosphate were dissolved in 0.42 liter of water. 1.6M of triethylenetetramine were added slowly while mixing. After the neutralization was complete, the mixture was heated to 150F and 1.6M of ethanedial were added. The mixture was then heated to l70-l75F. and allowed to cool to room temperature. The result was a water soluble polymer condensation product.

The aforedescribed condensation products are soluble in alkaline cyanide zinc plating baths. The addition of small amounts of the condensation products to alkaline cyanide zinc plating baths unexpectedly improves the appearance as by a zinc electrodeposit of improved brighteners. Beneficial results may be realized with the addition of as little as 0.01 grams of the brightener per liter, although ordinarily noticeable improvements will not be realized until at least 0.5 grams per liter of condensation product to bath are employed. The upper limits of the condensation product are dictated by economics and amounts above 20 grams per liter usually are unnecessary.

The alkaline cyanide zinc plating baths used in evaluating the water soluble polymer condensation products are well known to the art and are represented by the following compositions:

The following table illustrates the use of the reaction products as brightening agents in alkaline cyanide baths.

Condensation Condensation Product of Product Con- Current Density Range(Amps/ft Example centration Bath No. 1 Bath No. 2 Bath No. 3

No. l 1 g/l Semibright Semibright Semibright (2-25 amps/fi (2-25 amps/ft (1-20 amps/ft No. l 4 g/l Bright Bright Very bright (240) (2-50) (140) No. 2 4 g/l 1 Bright Bright Bright (2-30) (2-30) (2-35) No. 3 4 g/l Bright Bright Bright (2-40) (1-40) (2-35) No. 3 8 g/l Very bright Very bright Very bright Continued Condensation Condensation Product of Product Con- Current Density Rangc(Amps/ft Example ccntration Bath No. 1 Birth No. 2 Bath No. 3

No. 4 1 g/l Scmibright Scmihright Scmibright (2-20) (2-15) (l-ZO) No. 4 1 g/l Bright Bright Bright (2-35) (2-40) (l25l No. 4 8 g/l Very bright Very bright Very bright (Z40) (.1-45) (1-45) N0. 5 4 g/l Bri ht Bri ht Bri ht The advantages of the condensation products described above should be apparent. The water soluble condensation products when added to alkaline cyanide zinc plating baths produce lustrous bright deposits over wide current density ranges. The condensation prod ucts may be used in alkaline cyanide zinc plating baths whether of high, low, or medium cyanide contents. The effectiveness in low cyanide baths is especially important. The alkaline high cyanide zinc plating baths are reduced to medium cyanide zinc plating baths and then to alkaline low cyanide zinc plating baths and it is an advantage of the invention that the reaction products can in many cases maintain the same brightening effect throughout such changes.

The condensation products of the invention may be used alone or in conjunction with other adjuvents or with other brightening agents. They represent a novel composition of matter and although they demonstrate some particular advantages in the alkaline cyanide baths, their use is not limited thereto.

There has been set forth preferred embodiments of the invention, and although specific terms are employed, these are used in a generic and descriptive sense only, and not for the purpose of limitation. Changes in form and proportion of parts, as well as substitution of equivalents are contemplated, as circumstances may suggest or render expedient, without departing from the spirit and scope of this invention, as further defined in the following claims.

I claim:

1. An aqueous, alkaline zinc cyanide electroplating bath containing as brightening agents, the polyaminedialdehyde condensation products prepared by reacting at least one aliphatic dialdehyde with at least one polyamine salt of a water-soluble acid at temperatures and for a time sufficient to form said reaction products, said polyamine of said polyamine salt being a water soluble aliphatic compound having at least two terminal amine groups, said aliphatic dialdehyde being water soluble and having two terminal aldehyde groups, and said polyamine-dialdehyde condensation products present in sufficient amounts to improve the brightening of the plated products and characterized by solubility in said alkaline zinc cyanide bath.

2. The composition of claim 1 in which said polyamine is of the formula:

in which R is an aliphatic chain containing from 2 to 5 carbon atoms between said terminal amine groups, and in which R and R" are selected from the class consisting of hydrogen and aliphatic substituent groups.

3. The composition of claim 1 in which said polyamine comprises a diamino alkane.

4. The composition of claim 1 in which said polyamine comprises a polyethylene polyamine.

5. The composition of claim 1 in which said dialdehyde is of the formula:

in which R is an aliphatic group having from O to 3 carbon atoms in the chain linking the terminal aldehyde groups.

6. The composition of claim 1 in which said dialdehyde is an alkanedial.

7. The composition of claim 1 in which said salt comprises the polyamine of a water soluble inorganic acid which forms stable electrovalent bonds with the polyamine that do not decompose when heated during preparation and use.

8. The composition of claim 1 in which said salt comprises the polyamine of an alkali metal sulfate.

9. The composition of claim 1 in which said salt comprises the polyamine of sodium acid sulfate.

10. The composition of claim 1 in which said salt comprises the polyamine of a water soluble organic acid which forms stable electrovalent bonds with the polyamine that do not decompose when heated during preparation and use.

11. The composition of claim 1 in which said salt is the polyamine of citric acid.

12. In the process of electrodepositing zinc from an aqueous, alkaline zinc cyanide electroplating bath, the improvement which comprises adding to the bath a brightening composition comprising the polyaminedialdehyde condensation products prepared in accordance with the process comprising:

forming a polyamine salt by admixing a water soluble acid with a water soluble polyamine,

said polyamine having at least two aliphatic terminal amine groups,

reacting with said polyamine salt a water soluble dialdehyde at temperatures and for a time sufficient to form polyamine-dialdehyde products. 

1. AN AQUEOUS, ALKALINE ZINC CYANIDE ELECTROPLATING BATH CONTAINING AS BRIGHTENING AGENTS, THE POLYAMINE-DIALDEHYDE CONDENSATION PRODUCTS PREPARED BY REACTING AT LEAST ONE ALI PHATIC DIALDEHYDE WITH AT LEAST ONE POLYAMINE SALT OF A WATERSOLUBLE ACID AT TEMPERATURE AND FOR A TIME SUFFICIENT TO FORM SAID REACTION PRODUCTS, SAID POLYAMINE OF SAID POLYAMINE SALT BEING A WATER SOLUBLE ALIPHATIC COMPOUND HAVING AT LEAST TWO TERMINAL AMINE GROUPS, SAID ALIPHATIC DIALDEHYDE BEING WATER SOLUBLE AND HAVING TWO TERMINAL ALDEHYDE GROUPS, AND SAID POLYAMINE-DIALDEHYDE CONDENSATION PRODUCTS PRESENT IN SUFFICIENT AMOUNTS TO IMPROVE THE BRIGHTENING OF THE PLATED PRODUCTS AND CHARACTERIZED BY SOLUBILITY IN SAID ALKALINE ZINC CYANIDE BATH.
 2. The composition of claim 1 in which said polyamine is of the formula:
 3. The composition of claim 1 in which said polyamine comprises a diamino alkane.
 4. The composition of claim 1 in which said polyamine comprises a polyethylene polyamine.
 5. The composition of claim 1 in which said dialdehyde is of the formula: OCH-R-CHO in which R is an aliphatic group having from 0 to 3 carbon atoms in the chain linking the terminal aldehyde groups.
 6. The composition of claim 1 in which said dialdehyde is an alkanedial.
 7. The comPosition of claim 1 in which said salt comprises the polyamine of a water soluble inorganic acid which forms stable electrovalent bonds with the polyamine that do not decompose when heated during preparation and use.
 8. The composition of claim 1 in which said salt comprises the polyamine of an alkali metal sulfate.
 9. The composition of claim 1 in which said salt comprises the polyamine of sodium acid sulfate.
 10. The composition of claim 1 in which said salt comprises the polyamine of a water soluble organic acid which forms stable electrovalent bonds with the polyamine that do not decompose when heated during preparation and use.
 11. The composition of claim 1 in which said salt is the polyamine of citric acid.
 12. In the process of electrodepositing zinc from an aqueous, alkaline zinc cyanide electroplating bath, the improvement which comprises adding to the bath a brightening composition comprising the polyamine-dialdehyde condensation products prepared in accordance with the process comprising: forming a polyamine salt by admixing a water soluble acid with a water soluble polyamine, said polyamine having at least two aliphatic terminal amine groups, reacting with said polyamine salt a water soluble dialdehyde at temperatures and for a time sufficient to form polyamine-dialdehyde products. 